Skip to content

6.6 Gene Expression and Cell Specialization

Keywords

English Term 中文翻译 Definition & Explanation
Transcription Factors 转录因子 Proteins that bind to DNA and help regulate the initiation of transcription.
Promoter 启动子 A specific DNA sequence where RNA polymerase binds to begin transcribing a gene.
Enhancer 增强子 DNA sequences that, when bound by specific transcription factors, increase the rate of transcription.
Repressor 阻遏蛋白 A regulatory protein that binds to DNA and inhibits transcription.
Cell Specialization 细胞特化 The process by which cells develop into specific types with distinct functions.
Small RNAs 小分子 RNA Functional RNA molecules (like miRNA and siRNA) that can inhibit gene expression.

1. Initiation of Transcription

The regulation of gene expression primarily occurs at the level of transcription initiation. This process is governed by the interaction between DNA sequences and regulatory proteins.

  • Regulatory Sequences:
    • Promoters: Located immediately upstream of the transcription start site.
    • Enhancers: Can be located far upstream or downstream of the gene.
  • Binding Events: RNA polymerase and specific transcription factors must bind to these sequences to initiate the assembly of the transcription complex.

2. Positive vs. Negative Regulation

Gene expression is controlled by the balance of "gas pedals" and "brakes."

  • Positive Regulation: Activator proteins bind to enhancer sequences, stimulating or increasing the rate of transcription.
  • Negative Regulation: Negative regulatory molecules (repressors) inhibit gene expression by binding to specific DNA sequences (like operators in prokaryotes or silencers in eukaryotes), physically blocking RNA polymerase from transcribing the gene.

3. Differential Gene Expression and Specialization

Every somatic cell in an organism contains the exact same genome. However, a heart cell and a brain cell have vastly different structures and functions.

  • Differential Gene Expression: The process by which cells express different subsets of their genes.
  • Mechanism: Cell specialization is influenced by the specific combination of transcription factors present in the cell, which determines which "cell-specific" proteins are produced.
  • Outcome: This influences the cell's products, functions, and ultimately its identity.

4. Regulation by Small RNA Molecules

Not all regulation happens at the DNA level. Certain small RNA molecules (such as miRNA and siRNA) play a crucial role in post-transcriptional regulation.

  • These molecules can bind to complementary sequences on mRNA transcripts.
  • Result: They can either trigger the degradation of the mRNA or block its translation by the ribosome, effectively silencing the gene.

Quiz

Campbell Biology Chapter 18 Practice Test: Control of Gene Expression

Click the link above to practice related multiple-choice questions (opens in a new tab).